Generally, air-fuel ratio control in a gas engine is adapted to fuel gas having a predetermined composition. However, the composition of fuel gas actually supplied is not fixed, accordingly, the calorific value of the fuel gas also varies.
Conventionally, a gas engine is proposed, which has a configuration in which the fuel gas is measured using a gas composition measurement device such as a gas chromatography detector so that the air-fuel ratio is controlled according to measured results (for example, see Patent Document 1).